1. Technical Field
The present disclosure relates to the forming of insulating trenches. More particularly, the present disclosure relates to the forming of insulated trenches filled with a conductive material.
2. Description of the Related Art
Electronic components, and in particular pixels, formed in a semiconductor substrate are generally separated from one another by insulating structures. A type of insulating structure comprises a trench having its walls covered with an insulating coating, the trench being filled with a conductive material.
FIG. 1 is a simplified cross-section view showing an example of a device comprising such insulating trenches and a transistor extending between two trenches. Two trenches 1 are formed in a semiconductor substrate 3. The walls of each trench are covered with an insulating coating 5. Each trench is filled with a conductive material 7 having an upper portion 9 protruding above the upper surface of substrate 3. In operation, a fixed bias voltage is applied to conductive material 7 of the trench.
A transistor for which only the gate has been shown is formed between the two trenches. Conductive gate 11 covers a portion of a gate insulator layer 13. The gate extends between the two trenches 1, each end of the gate being arranged above upper portion 9 of conductive material 7 of a trench 1. In operation, gate 11 is alternately set to a high voltage and to a low voltage.
At the level of an upper portion 9 of conductive material 7, gate 11 is separated from conductive material 7 by insulating layer 13 having a thickness generally lower than 10 nm. There thus is a strong stray capacitance between gate 11 and conductive material 7.
Further, due to the small thickness of gate insulator layer 13 and to the topography of upper portion 9 of conductive material 7 of each trench 1, cracks may appear in gate insulator layer 13, more particularly at the upper corners of portion 9. Such cracks in gate insulator layer 13 may cause short-circuits between gate 11 and conductive material 7.
It would be desirable to provide a structure avoiding such disadvantages.
There further exist devices comprising deep insulation trenches, currently called DTI (Deep Trench Insulation) trenches and shallower trenches currently called STI (Shallow Trench Insulation) trenches. DTI trenches, for example the trenches of FIG. 1, generally penetrate by more than 2 μm into the substrate and STI trenches generally penetrate by less than 1 μm into the substrate, STI trenches being filled with an insulating material, for example, silicon oxide.
In such devices, it is desirable, particularly for the implementation of photolithography methods, for the upper surfaces of the materials filling the various trenches to be at the same level.